Re: [math-fun] Primes of the form 1+2*p^k
1+2*251^251 is prime. Lisp's integer-length returns 2002 bits. 251 = 1+2*5^3 and is prime. Kinda cool!
1+2*5^0=3 is prime, 1+2*5^3=251 is prime, 1+2*5^251 is prime, ... ? ... (Maybe this progression was implicit in Henry's post, but I thought it deserved explicit mention.) Jim Propp On Sunday, October 25, 2015, Henry Baker <hbaker1@pipeline.com> wrote:
1+2*251^251 is prime. Lisp's integer-length returns 2002 bits.
251 = 1+2*5^3 and is prime.
Kinda cool!
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1 + 2 * 5^251 is definitely not prime; it's divisible by 7. Henry's post pertained to the very different number 1 + 2 * 251^251.
Sent: Sunday, October 25, 2015 at 1:49 PM From: "James Propp" <jamespropp@gmail.com> To: math-fun <math-fun@mailman.xmission.com> Subject: Re: [math-fun] Primes of the form 1+2*p^k
1+2*5^0=3 is prime, 1+2*5^3=251 is prime, 1+2*5^251 is prime, ... ? ...
(Maybe this progression was implicit in Henry's post, but I thought it deserved explicit mention.)
Jim Propp
On Sunday, October 25, 2015, Henry Baker <hbaker1@pipeline.com> wrote:
1+2*251^251 is prime. Lisp's integer-length returns 2002 bits.
251 = 1+2*5^3 and is prime.
Kinda cool!
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participants (3)
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Adam P. Goucher -
Henry Baker -
James Propp